As wireless data transmission will become more common in the future and the number of users will grow, it is essentially important to increase the capacity of systems by improving their performance. A way of enhancing the performance of a radio system is to allocate radio resources using beam forming in the transmission and reception of a base station. Beam forming is typically implemented using antenna arrangements consisting of one or more antenna elements used both in transmission and reception, and by weighting the signals of the antenna elements. The beam patterns resulting from beam forming typically comprise two or more antenna beams, which can further be associated with beam-specific coding. In an ideal case, each beam thus enables a separate physical radio channel, which reduces the multi-user interference that impairs the performance of the radio system.
Allocation of the radio resources to user equipment is typically based on uplink channel measurements carried out by the base station on signals transmitted by the user equipment. Selection of a favourable portion of the cell in the downlink is based on correspondence between the uplink and downlink antenna beam patterns such that each uplink beam has a corresponding downlink counterpart. Therefore, it can be assumed that the best downlink channel can be obtained using the antenna beams that provide the best uplink channel.
However, the correspondence between the downlink and uplink beam patterns causes inflexibility when optimising the downlink and uplink beam structures in terms of overall capacity of the telecommunication system.